In restaurant kitchens fume hoods are necessary to remove cooking odors, especially over deep fat and grease frying equipment where the fumes include a considerable amount of contaminants in the exhaust.
Prior art systems include an exhaust fan and a hood system for drawing air from over a cooking surface into the hood and out an outlet. They sometimes include screens or filters for collecting the grease. Since such screens require considerable cleaning, the preferred system has been to let the grease be eliminated from the air by having it stick to inside surfaces of the hood interior surfaces. This not only is an inefficient and unsatisfactory method of removing the grease, but also, because of the heat involved, the grease tends to bake onto the inner surface of the hood and is difficult to remove. This also creates a possibility of fire. In fact, most fire codes and underwriters laboratories require a spring-loaded fire damper to close the top exit of the hood in the event of fire.
In systems such as these, the inside of the hood is cleaned when the hood is not being operated by using one or more spray nozzles permanently mounted inside the duct to scrub down the baked on grease. This can only be done when the exhaust fan is turned to off.
A variation on this prior art technique is a system in which one or possibly more spray nozzles are mounted somewhere within the hood. These operations conducted while the hood is in operation have the purpose of cooling the air so that better condensation of the grease on the sides of the hood will be obtained. Normally, this provides only nominal air-water contact so only a small amount of grease will actually be removed by the water. To the extent that grease removed by the water could cause clogging unless there is a periodic detergent cycle in which a fan is turned off; otherwise the grease may be carried in water droplets and stick to the ducts and fan blade that moves air through the hood.
"Waterfalls" have been used in industrial air scrubbers, in association with other steps, but normal waterfalls are subject to being "punctured" by an air stream, i.e., develop holes or voids in the waterfall permitting much of the contaminated air to pass through the holes without contacting the water. See, for example, the patents to Fisher, U.S. Pat. Nos. 2,259,032 and 2,354,674, and McIllvaine U.S. Pat. No. 3,077,714.
U.S. Pat. No. 4,351,652 provides a very efficient system of grease removal from an air stream. However, it has been determined that the spray nozzles within the housing tend to become contaminated and clogged with minerals in the water and coated with grease over a period of time and it is time consuming to open the hood to clean the nozzles, and one does not know when these nozzles plug up.
Accordingly, the present invention provides a new and improved fume hood which effectively removes grease and other contaminants from an air stream and which is easily maintainable without opening the fume hood for removable and/or cleaning of inside nozzles or the inside walls of the hood, or with visual contact of the water fall to insure continuing efficient extraction of the grease.